Equine and porcine uteroferrine will be stuided to compare biochemical properties and determine mechanism(s) of placental transport. Proteases and protease inhibitors, especially plasminogen activator inhibitor, will be purified from porcine uterine secretions and characterized. Glucose-6-PO4 dehydrogenase and sorbitol dehydrogenase enzymes will be studied during the period of blastocyst placentation in pigs to establish possible hormonal regulation of these enzymes in the endometrium. The effect of estrogen on endometrial metabolism of progesterone to androgens and estrogens will be evaluated to determine whether or not estrogens of blastocyst orgin may influence endometrial steroid metabosism and, in turn, endometrial steroid metabolism and, in turn, endometrial protein secretions.